Generally, a microwave oven is a device that is used to heat food by radiating microwave generated from a magnetron to the food when electric current is applied to electric components of the device. Such a microwave oven is classified into a household microwave oven having a small magnetron and a commercial microwave oven having a large (or a plurality of) magnetron(s).
The microwave oven is further classified according to a heating method into a glass tray method rotating the food and a stirrer fan method scattering microwave radiated into the cavity. The former is generally applied to the household microwave oven while the latter is applied to the commercial microwave oven. Meanwhile, since the commercial microwave oven is generally used at convenience stores where the microwave oven is frequently used and restaurants where a large amount of the food should be quickly heated, the commercial microwave oven needs relatively high power output compared with the household microwave oven.
Since the microwave oven cooks the foods by radiating the high power microwave into a cavity, it should be careful so that the microwave cannot be radiated when a door is in an opened state. If the microwave is radiated when the door is in the opened state, a fatal accident threatening user's safety may be caused.
In order to control the radiation of the microwave depending on the opened/closed state of the door in the microwave oven, a latch is provided at an inside of the door of the microwave oven and a latch board is provided at a front side of the microwave oven. An operation of the latch board is controlled by the latch. In more detail, the latch board fixes the latch such that an automatic opening of the door is prevented. Also, when the latch is inserted and locked into the latch board, the closing of the door is correctly detected and the operations of the magnetron and the microwave oven are controlled.
An operation of the latch board will now be described in brief. A motor switch and a circuit switch are provided on the latch board. The circuit switch is provided with one primary switch and one secondary switch. The monitor switch controls the on/off operation of the monitor of the microwave oven and the circuit switch controls the on/off operation of other drive circuits, including the magnetron, of the microwave oven.
Meanwhile, the switch performs the on/off operation in association with the insertion of the latch. That is, when the latch is inserted, the monitor switch is first turned off and the circuit switch is then turned on at predetermined time interval. Specifically, when the monitor switch is first turned off and the circuit switch is then turned on, a predetermined time difference occurs between the two switches. It aims to prevent the voltage applied to the primary switch from directly flowing through the secondary switch.
In the related art latch board, however, the time difference between the on/off of the monitor switch and the on/off of the circuit switch is short. Thus, the voltage applied to the primary switch frequently flows through the secondary switch directly, so that the circuit is shorted. Like this, if the circuit is shorted, a fuse is disconnected such that the microwave cannot be used any more until after service. Therefore, there is a demand for a latch board structure that can increase the difference in operation time of the monitor switch and the circuit switch.